Potentiodynamic and cyclic voltametric studies on the Passivity of Tin in neutral phosphate buffer

Passivity of tin has been investigated in phosphate buffer (pH 6.7) using potentiodynamic and cyclic voltammetric techniques. The formation of thin transparent electronically conducting passive film on which O₂ is evolved in the transpassive range is indicated. The solution remains clear. Potentiodynamic measurements performed from −1.2 to 2.5 V (SCE) and backward at scan rates between 1 and 100 mV/sec give one anodic peak. In the reverse scanning, two cathodic peaks appear at low scan rates and disappear completely at higher rates. Values of the open dircuit potential, the corrosion potentials Ecor (forward and reverse), the anodic peak potential Ep and the anodic peak cd Ip are recorded. The results are compared with our previous work in neutral chloride, bromide, iodide, and sulphate solutions. Thermodynamic data are used to predict the possible oxidized species constituting the anode film. Cyclic voltammetric measurements have been carried out in the potential range between H₂ and O₂ evolution, and in limited potential ranges at scan rates between 1 and 200 mV/sec. One anodic peak is detected in all cases. While a short arrest and a cathodic peak appear in the results between H₂ and O₂ evolution, two distinct cathodic peaks appear up to 100 mV/sec in the results taken between –1.2 and −0.224 V. Plots of Ip vs the square root of scan rate are linear, and indicate diffusion-controlled kinetics for the reactions initiating passivity. Linear relations are observed for Ep vs log scan rate indicating the irreversible nature of the anodic processes. While the formation of SnO and SnO₂ is predicted from thermodynamics at potentials more negative than Ep, the formation of Sn(OH)₄ is predicted at potentials more positive than Ep. The conclusions drawn from the results obtained with the two different techniques are generally the same. The results are compared with and discussed on the light of previous work using cyclic voltammetry.     

The anodic behaviour and Passivity of Tin in sulphate solutions

Passivation of spec-pure Sn was studied in aerated, unstirred solutions of acid sulphate (H₂SO₄/Na₂SO₄) and neutral suphate (Na₂SO₄) using the potentiodynamic technique from an initial cathodic potential (?ve to open circuit potential) in the anodic direction and backwards to the initial potential. Only one anodic peak is observed in all results. The effect of etching is manifested in pure 0.1 M H₂SO₄ and in the solution containing 75% acid and 25% by vol 0.1 M Na₂SO₄. In all solutions, a grayish white film devlops on the Sn anode, and a white precipitate is formed in solution. Data are complied for the corrosion potential Ecor, the cathodic and anodic Tafel slopes, the corrosion cd Icor, the peak potential and the peak cd for acid sulphate solutions. The effect of scan rate has been demonstrated in 0.1 M Na₂SO₄ in the range 1-100 m V/sec for unstirred and 1-50 m V/sec for stirred solutions. The plot of peak cd Icc (Ip) vs the square root of the scan rate gives a striaght line with positive slope indicating diffusion kinetics for the anode film formation. USe of thermodynamic data leads to the possible formation of SnO, SnO₂, Sn(OH)₂ and Sn(OH)₄ in the anode film. The limitations of the thermodynamic treatment is discussed. It is concluded that film formation is governed by a dissolution/precipitation mechanism based on diffusion kinetics. In the absence of the results of surface analysis, the anode film may be visualized to be composed of the oxides and hydroxides of Sn (thermodynamic evidence) together with sulphate anions (kinetic evidence). O₂ evolution has not been detected up to 2.5 V (SCE), and this throws some light on the poor electron conductance of the anode film, and the probable dominance of lonic conductance during film growth.     

Electrochemical Studies on the passive behaviour of tin in different buffer solutions

The effect of pH on the passivity of Sn has been investigated in buffered (phthalate-borate, and citrate phosphate buffer series), and in unbuffered phosphate solutions, using the cyclic voltammetric technique. Two anodic peaks; the first being more pronounced than the second, and on cathodic peak have been observed in the two buffer series at different scan rates and pH values. The anodic and cathodic peak current densities (I_p) and potentials (E_p) are functions of the scan rate (v) and the pH value. Plots of I_p against v^1/2 yield straight lines at each pH value. The effect of pH on I_p for the first anodic peak shows a shallow minimum in the near neutral and slightly alkaline range at all scan rates. Straight lines are also observed between E_p and v^1/2, the extrapolation of which to v = 0 gives the spontaneous (no polarization) oxidation or reduction potentials (E′ and E″). The absence of polarization effects in E′ and E″ make them the most suitable values for comparison with thermodynamic data. Therefore, the two straight lines obtained between E′ and E″ on one hand and the pH on the other hand to give an estimate of (i) the slope (dE°/dpH), and (ii) the value of E° at pH - 0 (from intercept). Comparison of the two experimental values with all available thermodynamic data for Sn(II) and Sn(IV) oxides and hydroxides shows that: (i) the first anodic peak represents the formation of Sn(OH)₂ from Sn and OH^?, (ii) the second anodic peak represents the formation of Sn(OH)₄ directly from Sn and OH^?, and (iii) the cathodic reduction peak correponds to the reduction of Sn(IV) oxidized species to Sn. The results in citratephosphate buffer have been treated in the same manner. However, the result of (dE°/dpH) and E° at pH = 0 deviate from thermodynamic data, because of the possible participation of other anodic reactions such as the formation of soluble Sn compounds, Sn complexes, and incorporation of anions in the anodic film.     

Sorption of radioiodine from aqueous solutions on layered double magnesium aluminum hydroxides at 300 K

Sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solutions at 300 K on solid layered double magnesium aluminum hydroxides (Mg-Al-LDH) in the carbonate (Mg-Al-LDH-CO₃) and nitrate (Mg-Al-LDH-NO₃) forms was studied. The distribution coefficients of ¹³¹I^? and ¹³¹IO ₃ ^? between solid Mg-Al-LDH-CO₃ and an aqueous solution after contact of these phases for 60 min are 38 and 34 ml g^?1, respectively. The distribution coefficients of ¹³¹I^? and ¹³¹IO ₃ ^? between solid Mg-Al-LDH-NO₃ and an aqueous solution, measured under the similar conditions, are about 5 ml g^?1. After contact of the solid and liquid phases for 14 h, the distribution coefficients of ¹³¹I^? and ¹³¹IO ₃ ^? between an aqueous phase and solid layered double magnesium aluminum oxides (Mg-Al-LDO) prepared by thermolysis of Mg-Al-LDH are 7999 and 7068 ml g^?1, respectively.     

Sorption of 131I− and 131IO 3 − from aqueous solution on nickel hydroxide at 20°C

Sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solution on solid Ni(OH)₂ at 20°C was studied. It was found that in sorption from aqueous solution, after 120-min contact of the liquid and solid phases at V/m = 500 ml g^?1, with an increase in the concentration of I^? and IO ₃ ^? from 10^?5 to 10^?3 M the distribution coefficients K _d decrease from 16.4 to 5.3 ml g^?1 for ¹³¹I^? and from 113.6 to 30.8 ml g^?1 for ¹³¹IO ₃ ^? . The influence of various anions (Cl^?, NO ₃ ^? , SO ₄ ^2? , and BO ₃ ^3? ) on sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solution on solid Ni(OH)₂ was studied. It was found that, with an increase in the concentration of these ions from 10^?5 to 10^?1 M, the distribution coefficients K _d of ¹³¹I^? and ¹³¹IO ₃ ^? decrease by a factor of 3–10.     

Photoelectrochemical properties of Re6Se8Cl2 a lamellar transition metal cluster compound

Photoelectrochemical properties of vapor-grown single crystals Re₆Se₈Cl₂ are presented; this Re₆Se₈Cl₂ is a n-type semiconductor with a direct bandgap of about 1.42eV, corresponding to a probable d-d phototransition. The material is not stable under prolonged illumination in aqueous acidic and basic solutions. Addition of a I^?/I^?₃ redox system in acidic solution increases the photopotential (very strongly) to 490mV, shifts 600mV cathodically the onset of the anodic photocurrent and improves considerably the stability of the Re₆Se₈Cl₂ photoanode. This behavior is analysed in relation to the d band semiconductor character of Re₆Se₈Cl₂.     

Behavior of 131I and 137Cs in the oil-water and oil-gas phase systems

The behavior of ¹³¹I and ¹³⁷Cs in various chemical forms in the oil-water and oil-gas phase systems and the sorption of these radionuclides from radioactive transformer oil onto various inorganic and organic sorbents was studied. The degree of the ¹³⁷Cs extraction depends neither on the time of contact of the oil with aqueous solutions nor on the ¹³⁷CsI concentration in the solution. Under all the experimental conditions, the degree of extraction of ¹³⁷Cs did not exceed 5%. The degree of ¹³¹I extraction from water by the oil depends on the chemical form of the radionuclide: ¹³¹I^?, ³¹IO ₃ ^? , or ¹³¹I₂. The maximal extraction (～70%) is observed for K¹³¹IO₃, and the minimal (～25%), for ¹³¹I₂. Granulated nanocomposites containing particles of carbon or NaX zeolite and Fizkhimin sorbents based on coarsely porous silica gel and containing Ag and Ni in 1: 4 ratio allow efficient removal of ¹³⁷Cs and ¹³¹I from spent transformer oil of GK grade.     

Growth and characterization of LiNiVO4 thin film cathode by pulsed laser deposition

Crystallized LiNiVO₄ thin films have been prepared by pulsed laser deposition and their physical and electrochemical properties have been studied. With the increase of deposition temperatures and oxygen pressures, the crystallization became better, but accompanied with large sizes of grains. The initial discharge capacity of the film deposited at 873 K and 40 Pa of oxygen was just around 7.2 μA h/cm² μm when it was cycled between 3.0 and 4.8 V with a current density of 10 μA h/cm². Cyclic voltammetry at a sweep rate of 0.1 mV/s showed a main anodic peak at 4.20 V, a weak anodic peak at 4.59 V and a cathodic peak located at 3.73 V. Based on the linear relationship between the peak currents of cathodic peaks and the square roots of scan rates, the diffusion coefficient was estimated to be about 2.3 × 10^− 15 cm²/s. Electrochemical impedance spectra revealed high charge-transfer resistance of Li-ion, such as about 9000 Ω at 4.0 V. The extremely slow Li-ion diffusion and high charge-transfer resistance indicate that the electrochemical reaction in LiNiVO₄ thin films is sluggish.     

Sorption of radioactive iodine from aqueous medium at 25°C on granulated sorbents containing nitrates of <Emphasis Type="Italic">d</Emphasis> elements

Sorption of various species of radioactive iodine from aqueous phase at 25°C with granulated sorbents based on silica gel of the MSKG type, containing nitrates of d elements, was studied. Sorbents containing Zn, Ni, Cu, and Co, both nonmodified and modified, have low distribution coefficients K _d for ¹³¹I^? and ¹³¹IO ₃ ^? (at V/m = 1000, K _d < 120 ml g^?1). Whereas nonmodified sorbents do not noticeably sorb I₂ from the aqueous phase (at V/m = 1000, K _d < 10 ml g^?1), their modified analogs adsorb molecular iodine species and have K _d ～ 170–250 ml g^?1 at V/m = 1000. The study of sorption of radioactive iodine species with granulated sorbents containing silver nitrate showed that nonmodified sorbents have relatively low distribution coefficients K _d for all species of radioactive iodine (at V/m = 1000, K _d < 100 ml g^?1). At the same time, the modified sorbents containing Ni and Ag sorb not only I₂ (at V/m = 1000, K _d ～ 270 ml g^?1) but also ¹³¹I^? and ¹³¹IO ₃ ^? ions from aqueous solutions (at V/m = 1000, K _d ～ 3100 and 1500 ml g^?1, respectively).     

An All‐Solution‐Based Hybrid CMOS‐Like Quantum Dot/Carbon Nanotube Inverter

The development of low‐cost, flexible electronic devices is subordinated to the advancement in solution‐based and low‐temperature‐processable semiconducting materials, such as colloidal quantum dots (QDs) and single‐walled carbon nanotubes (SWCNTs). Here, excellent compatibility of QDs and SWCNTs as a complementary pair of semiconducting materials for fabrication of high‐performance complementary metal‐oxide‐semiconductor (CMOS)‐like inverters is demonstrated. The n‐type field effect transistors (FETs) based on I^? capped PbS QDs (V _th = 0.2 V, on/off = 10⁵, S _S‐th = 114 mV dec^?1, µ _e = 0.22 cm² V^?1 s^?1) and the p‐type FETs with tailored parameters based on low‐density random network of SWCNTs (V _th = ?0.2 V, on/off > 10⁵, S _S‐th = 63 mV dec^?1, µ _h = 0.04 cm² V^?1 s^?1) are integrated on the same substrate in order to obtain high‐performance hybrid inverters. The inverters operate in the sub‐1 V range (0.9 V) and have high gain (76 V/V), large maximum‐equal‐criteria noise margins (80%), and peak power consumption of 3 nW, in combination with low hysteresis (10 mV).     

Electrochemical behaviour and voltammetric determination of sulphadiazine using a multi-walled carbon nanotube composite film-glassy carbon electrode

The anodic oxidation of sulphadiazine (SD) was investigated at a glassy carbon electrode modified by multi-walled carbon nanotube (MWCNT–GCE), using cyclic voltammetry and chronoamperometry. The results indicate that MWCNT-modified GCEs show an efficient and selective electrocatalytic activity towards the anodic oxidation of SD among biologically important compounds in buffered solutions at pH?=?7. It was found that oxidation of SD at the surface of MWCNT–GCE occurs at a potential less positive than that of unmodified GCE (about 100?mV). The diffusion coefficient of SD was also estimated using chronoamperometry. The kinetic parameters such as the electron transfer coefficient between SD and modified electrode, α, and the charge transfer rate constant, k_s , for oxidation of SD at the MWCNT–GCE surface were determined according to the Laviron procedure. The dissociation constants of oxidised and reduced acid–base species of SD can be obtained from the E _1/2 versus pH curves. The linear dependence of the peak current on the concentration was observed in the range 10–2000?µmol?L^?1 with a detection limit of 7.1?µmol?L^?1. The method was also applied to determinate the SD in human blood plasma and urine samples.     

Constructing Multifunctional Heterostructure of Fe2O3@Ni3Se4 Nanotubes

Heterostructures have attracted increasing attention due to their amazing synergetic effects, which may improve the electrochemical properties, such as good electrical/ionic conductivity, electrochemical activity, and mechanical stability. Herein, novel hierarchical Fe₂O₃@Ni₃Se₄ nanotubes are successfully fabricated by a multistep strategy. The nanotubes show length sizes of ≈250–500 nm, diameter sizes of ≈100–150 nm, and wall thicknesses of ≈10 nm. The as‐prepared Fe₂O₃@Ni₃Se₄ nanotubes with I_Ni:Fe = 1:10 show excellent Li storage properties (897 mAh g^?1 high reversible charge capacity at 0.1 A g^?1), good rate performance (440 mAh g^?1 at 5 A g^?1), and outstanding long‐term cycling performance (440 mAh g^?1 at 5 A g^?1 during the 300th cycle) as an anode material for lithium ion batteries. In addition, the Fe₂O₃@Ni₃Se₄ nanotubes with I_Ni:Fe = 1:10 (the atomic ratio between Ni and Fe) show superior electrocatalytic performance toward the oxygen evolution reaction with an overpotential of only 246 mV at 10 mA cm^?2 and a low Tafel slope of 51 mV dec^?1 in 1 m KOH solution.     

Electrochemical Deposition of Composites Using Deoxycholic Acid Dispersant

A biomimetic method has been used for the electrodeposition of carbon nanotubes (NTs) and composite films using a commercial bile acid. Thin films of deoxycholic acid (DCH) were prepared potentiodynamically and galvanostatically from deoxycholic acid sodium salt (DCNa) solutions. The anodic deposition yield has been investigated at different DCNa concentrations. The electrodeposition mechanism involved electromigration of anionic DC^? species, local pH reduction at the anode, and precipitation of DCH. It was found that DCNa allowed excellent dispersion of NTs in water. The use of DCNa as a multifunctional agent for NTs dispersion, charging, and binding allowed electrodeposition of NTs and composite MnO₂–NTs films. The MnO₂–NTs composites were used for charge storage applications in supercapacitors. The MnO₂–NTs electrodes showed good capacitive behavior. DCNa is a promising charging dispersant for NTs dispersion and manufacturing of other composites by electrochemical methods.     

Lower Oxidation States of <Emphasis Type="Italic">f</Emphasis> Elements: III. Properties of Low-Valence Lanthanide and Actinide Compounds in the Solid State and in Various Solvents

Properties of low-valence f-element compounds in the solid state and in protic, aprotic, and mixed solvents are discussed, including the solubility of low-valence f-element compounds, hydration of Ln²⁺ and An²⁺, and their complexation in aqueous and organic solutions with various anions (I^?, Br^?, Cl^?, ClO ₄ ^? , BF ₄ ^? , BPh ₄ ^? and polycyclic crown ethers.     

Anodic oxidation and stress corrosion cracking (SCC) of titanium alloys

Uniform and reproducible oxide films were formed on alloy Ti-6Al-6V-2.5Sn by anodic oxidation in aqueous 0.5% H₃BO₃, at 10 mA cm⁻² and voltages up to 110V; dielectric break down occurred above 120V. A parallelism was found between the effect of environmental factors on stress corrosion cracking (SCC), as reported in the literature and the anodic behaviour, as observed by ourselves: factors that increased susceptibility to SCC (increase in temperature or viscosity, alloying, introductions of CI⁻ or methanol, lowering of pH) reduced passivity under anodic polarization, while factors that inhibited SCC (thicker oxide films, high pH, phosphate ions) increased passivity. The passivity was associated both with the presence of the anodic oxide and with a transitory effect of the electric field across the oxide and the oxide-electrolyte interface.     

Evidence for the activation-controlled galvanostatic growth of thin Anode Films on Tin in some neutral media

Growth of thin transparent anode films on Sn in neutral media has been studied by measuring galvanostatic anodic charging curves in phosphate buffer, 0.1M KCl and 0.1M Na₂SO₄ solutions (pH 6.6–6.7) at low current densities. The experimental technique is essentially the same as that used in previous investigations on valve metals. Although the rise in the anode potential of Sn does not exceed 2.0 V, the shape of the anodic charging curve is identical to that observed on valve metals: being thus composed of a linear and a non-linear region. Application of the kinetics of galvanostatic anodization to the results on Sn show that: (i) the oxide formation rate is linearly related to the ionic current density i by a double logarithmic plot, (ii) the reciprocal capacity is linearly related to log i, and (iii) the Tafel behaviour is exhibited at constant charge. These relations indicate that the anode film growth occurs by an activation-controlled ion conduction under the influence of the electric field across the film phase according to an exponential law. Treatment of the results allows the estimation of some kinetic parameters of film growth, e.g.: (i) the constants a and b of the empirical relation between oxide formation rate and i, (ii) the constants A and B of the exponential law, (iii) the electric field which is of the order of 10⁶ V/cm in phosphate, and 10⁷ V/cm in both chloride and sulphate solutions, and (iv) the effective activation distance for the ionic jump over the energy barrier associated with cation transport within the film, whereupon relative (and not absolute) values can only be obtained. Comparison between the present results and previous ones (also on Sn) taken by potentiodynamic technique shows that while diffusion kinetics play an important role in the formation of thick anode films by the potentiodynamic technique, activation-controlled kinetics explain the present results on the galvanostatic formation of thin transparent anode films.     

Properties of amorphous Si thin film anodes prepared by pulsed laser deposition

Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100 μA/cm² in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5 V at various scan rates from 0.1 to 2 mV/s. The apparent diffusion coefficient (D_Li) calculated from the CV measurements was about ∼10⁻¹³ cm²/s. The Si thin film anode was also successfully coupled with LiCoO₂ thin film cathode. The a-Si/LiCoO₂ full cell showed stable cycle performance between 1 and 4 V.     

Simultaneous doping of anodic silicon oxide films with phosphorus and arsenic

It is established that, during the formation of anodic P- or As-doped SiO₂ films on p-Si in an ethylene glycol + 0.13% H₂O solution containing 14.3% H₃PO₄, 0.17% HNO₃, and 0.0193–1.95% H₃AsO₄ additives, the orthophosphoric and orthoarsenic acids do not produce any combined effect upon the process of introduction of the arsenate and phosphate anions into silicon dioxide. It is suggested that the partial anodic reactions of Si with NO ₃ ^? , OH^?, AsO ₄ ^3? , and PO ₄ ^3? proceed with the formation of SiO₂ involving As₂O₃, As, As₂O₅, P₂O₅, and P.     

Sorption of Radioactive Iodine on Polymeric Sorbents from Aqueous Solutions and Gas Phase

Sorption of various species of radioactive iodine from aqueous and gas phases on polymeric sorbents Styrosorb and Polysorb-1 was studied. These sorbents do not take up ionic species of radioactive iodine (¹³¹I^- and ¹³¹IO₃ ^-) from aqueous solutions. At the same time, both sorbents take up ¹³¹I₂ from aqueous solutions at 25°C. At V/m = 500 ml g^{- 1}, the distribution factors K _d are 1350 and 590 ml g^{- 1} with Styrosorb and Polysorb-1, respectively. These sorbents efficiently recover ¹³¹I₂ from an air flow at 25°C and flow velocity of 0.33 cm s^{- 1}. The sorption capacity of Styrosorb is approximately four times higher than that of Polysorb-1 and amounts to 97.0 mg of I₂ per gram of sorbent. These data are consistent with the specific surface areas of the sorbents.     

Vertical ZnO Nanotube Transistor on a Graphene Film for Flexible Inorganic Electronics

The bottom‐up integration of a 1D–2D hybrid semiconductor nanostructure into a vertical field‐effect transistor (VFET) for use in flexible inorganic electronics is reported. Zinc oxide (ZnO) nanotubes on graphene film is used as an example. The VFET is fabricated by growing position‐ and dimension‐controlled single crystal ZnO nanotubes vertically on a large graphene film. The graphene film, which acts as the substrate, provides a bottom electrical contact to the nanotubes. Due to the high quality of the single crystal ZnO nanotubes and the unique 1D device structure, the fabricated VFET exhibits excellent electrical characteristics. For example, it has a small subthreshold swing of 110 mV dec^?1, a high I_max/I_min ratio of 10⁶, and a transconductance of 170 nS µm^?1. The electrical characteristics of the nanotube VFETs are validated using 3D transport simulations. Furthermore, the nanotube VFETs fabricated on graphene films can be easily transferred onto flexible plastic substrates. The resulting components are reliable, exhibit high performance, and do not degrade significantly during testing.